Method of delivering liquid sterilant to a sterilizer

ABSTRACT

A method of delivering a liquid sterilant to a sterilizer involves piercing a cell of a cassette with a first needle having a first lumen, flowing a gas into the cell to pressurize the cell relative to a pressure within the first lumen and drive the liquid sterilant out of the cell through the first lumen. The liquid sterilant travels from the lumen to a vaporizer in the sterilizer.

BACKGROUND OF THE INVENTION

This application relates to the delivery of sterilant from a cassette toan instrument sterilizer, and more particularly to the extraction ofsterilant from the cassette.

One popular method for sterilizing instruments, such as medical devices,is to contact the devices with a vapor phase chemical sterilant, such ashydrogen peroxide. In many such sterilizers, it is preferred to deliverthe sterilant in liquid form and vaporize it in the sterilizer. Oneparticularly convenient and accurate method for delivering the liquidsterilant is to put a predetermined quantity of sterilant into acassette and deliver the cassette to the sterilizer. The sterilizer thenautomatically extracts the sterilant from the cassette and uses it forsterilization procedure. Typically, such a cassette would entailmultiple cells containing equal amounts of liquid sterilant with asterilization procedure employing the sterilant from one or more cells.Such a system is currently available in the STERRAD® sterilizationsystem available from Advanced Sterilization Products in Irvine, Calif.

U.S. Pat. Nos. 4,817,800; 4,869,286; 4,899,519; 4,909,287; 4,913,196;4,938,262; 4,941,518; 5,882,611; 5,887,716; and 6,412,340, eachincorporated herein by reference, disclose such cassettes and a methodfor draining liquid sterilant from a cell within a cassette. In essence,the cassette travels horizontally with a horizontally oriented cell andone or more needles pierces the cell from below while compressed air isapplied to an upper surface of the cassette cell. The cell is made froma flexible material so that the air compresses the cell and forces thesterilant out through the needles. Such a system limits the cassettedesign to an outer shell providing rigidity enclosing an inner cell of aflexible material. Further, the cell needs to be designed carefully toallow a complete collapse without trapping any of the liquid sterilantwithin a wrinkle in the cell during its collapse.

The present invention overcomes these and other limitations of the priorart.

SUMMARY OF THE INVENTION

A method, according to the present invention, of delivering a liquidsterilant to a sterilizer comprises the steps of: a) piercing a cell ofa cassette with a first needle having a first lumen, b) flowing a gasinto the cell to pressurize the cell relative to a pressure within thefirst lumen and drive the liquid sterilant out of the cell through thefirst lumen, and c) flowing the liquid sterilant from the lumen to avaporizer in the sterilizer.

In one aspect of the invention, a second lumen through the first needleopens into the gas is injected into the cell through the second lumen.In another aspect of the invention, the method includes the steps ofpiercing the cell with a second needle having a second lumen opening sothat the lumen opens into the cell and injecting the gas into the cellthrough the second lumen.

In one aspect of the invention, the gas is at atmospheric pressure andthe first lumen is at a pressure below atmospheric pressure. In anotheraspect of the invention, the gas is at a pressure greater thanatmospheric pressure.

The method is suitable for use with cassettes having multiple cells andsteps a), b) and c) can be repeated therewith.

Preferably, the liquid sterilant comprises hydrogen peroxide.

In one aspect of the invention, in step a) the needle enters the celllaterally. In another aspect of the invention, in step a) the needleenters the cell at an upper portion thereof and travels downwardlytherein. The needle can be positioned such that the first lumen opensinto the cell at or near its lowest point to maximize extraction ofliquid sterilant from the cell, or at a predetermined vertical positionto extract the liquid sterilant above the predetermined position, suchthat less than a total amount of liquid sterilant in the cell is thusextracted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a sterilizer employing a cassette handlingsystem according to the present invention;

FIG. 2 is a rear perspective view of a cassette handling systemaccording to the present invention;

FIG. 3 is a front perspective view of the cassette handling system ofFIG. 2;

FIG. 4 is a front perspective view of the cassette handling system ofFIG. 2 showing a spent cassette collection box;

FIG. 5 is a rear perspective view of the cassette handling system ofFIG. 2 showing its carriage in the insert position;

FIG. 6 is a rear perspective view of the cassette handling system ofFIG. 2 showing its carriage as it moves toward the home position;

FIG. 7 is a rear perspective view of the cassette handling system ofFIG. 2 showing its carriage in position to read a bar code on thecassette;

FIG. 8 is a rear perspective view of the cassette handling system ofFIG. 2 showing its carriage in the home position;

FIG. 9 is a front perspective view of the cassette handling system ofFIG. 2 showing its carriage in position to tap the cassette's firstcell;

FIG. 10 is a cross sectional view of the cassette showing a celltherein;

FIG. 11 is a front perspective view of the cassette handling system ofFIG. 2 showing upper and lower needles on an extractor subsystempenetrating the first cell of the cassette;

FIG. 12 is a front perspective view of the cassette handling system ofFIG. 2 showing upper and lower needles on the extractor subsystem inposition to penetrate the last cell of the cassette;

FIG. 13 is a front perspective view of the cassette handling system ofFIG. 2 showing the cassette being ejected therefrom;

FIG. 14 is a flow chart of the cassette handling process;

FIG. 15 is a rear perspective view of an alternative embodiment of acassette handling system of the present invention employing RFIDtechnology;

FIG. 16 is a memory map of an RFID tag of the cassette shown in FIG. 15;

FIG. 17 is a top plan view of an unfolded blank for forming the spentcassette collection box of FIG. 4; and

FIG. 18 is a perspective view of the blank of FIG. 17 folded to form thespent cassette collection box.

DETAILED DESCRIPTION

FIG. 1 shows in block diagram form a vapor phase sterilizer 10 employinga cassette handling system 12 according to the present invention. Thesterilizer 10 comprises a vacuum chamber 14 and a vacuum pump 16 forexhausting atmosphere therefrom. A vaporizer 18 receives liquidsterilant from the cassette handling system 12 and supplies it in vaporform to the vacuum chamber 14. A screen grid electrode 20 is providedwithin the vacuum chamber 14 for exciting the contents into the plasmaphase during a portion of the sterilization cycle. A micro filtered vent22 and valve 24 allow sterile air to enter the vacuum chamber 14 andbreak the vacuum therein. A control system 28 ties in to all of themajor components, sensors and the like within the sterilizer 10 tocontrol the sterilization cycle.

A typical sterilization cycle might include drawing a vacuum upon thevacuum chamber 14 and turning on power to the electrode 20 to evaporateand extract water from the vacuum chamber 14. The electrode 20 is thenpowered off and a low vacuum of less than 1 torr drawn on the vacuumchamber 14. Sterilant, such as hydrogen peroxide solution, is vaporizedby the vaporizer 18 and introduced into the vacuum chamber 14 where itdiffuses into contact with the items to be sterilized and killsmicroorganisms thereon. Near the end of the cycle, power is againapplied to the electrode 20 and the sterilant is driven into the plasmaphase. The electrodes 20 are powered down and filtered air is drawn inthrough the valve 24. This process can be repeated.

Turning also to FIGS. 2 to 4, the cassette handling system 12 accordingto the present invention is shown. It comprises in gross; a carriage 32for holding a cassette 34, a lead screw 36 and motor 38, an extractorsubsystem 40 and a scanner 42.

The carriage 32 comprises a bottom panel 44, a side panel 46 and toppanel 48 along with small vertical flanges 50 and 52 on the top andbottom and top panels 48 and 44, respectively, to capture the cassette34. The bottom, side and top panels 44, 46 and 48 flare outwardly at anentrance 54 of the carriage to aid in insertion of the cassette 34. Twospring catches 56 on the flanges 50 and 52 engage irregular surfaces ofthe cassette 34 to firmly position the cassette 34 within the carriage32.

The carriage 32 travels along the lead screw 36 and is supported on anupper rail 58. A lead screw nut 60 attached to the bottom panel 44 andhaving a threaded opening 62 and an unthreaded opening 63 receives thelead screw 36 and effects horizontal movement of the carriage 32 inresponse to rotations of the lead screw 36. Flanges 64 extend outwardlyfrom the top panel 48 and flanges 66 extend outwardly from the sidepanel 46 each having openings 69 for receiving the upper rail 58. Themotor 38 is preferable a stepping motor and connects to the lead screw36 to precisely control the horizontal position of the cassette 34relative to a frame 68.

The extraction assembly 40 comprises an upper needle 70 and a lowerneedle 72, each being of a lumened configuration. The upper needleconnects to an air pump 74 which can force air out through the upperneedle 70. The lower needle 72 connects to a valve 76 and from there isplumbed to the vaporizer 18.

The scanner 42 is oriented so as to be able to read a barcode 80 on thecassette 34 as well as a barcode 82 on a spent cassette collection box84. Upon insertion of the cassette 34 into the carriage 32 the scanner42 reads the cassette barcode 80. The barcode 80 is preferably encodedwith information regarding the contents of the cassette 34, includinglot numbers and expiration dates. This information can be used todetermine whether the cassette 34 is fresh and of the correct type andwhether the cassette 34 has been used in the system before and thus isat least partially empty. The code is communicated to the control system28 which makes these determinations.

The scanner 42 can also see the spent cassette collection box barcode 82when the carriage 32 moves inwardly and away from the scanner 42. Eachspent cassette collection box 84 preferably has two barcodes 82, one ineach opposing corner so that the scanner 42 can see one of themregardless of which end of the spent cassette collection box 84 isinserted first. With the spent cassette collection box 84 filled, thespent cassettes 34 block the barcode 82 which alerts the control system28 that there is no capacity for receiving additional spent cassettes34. Preferably this message will be output to a user, such as on adisplay screen (not shown). If the cassette 34 is empty it will not beejected and no new cycles will be run until a spent cassette collectionbox 84 having capacity to receive a spent cassette 34 is placed into thesterilizer 10.

A forward flag 86 and rearward flag 88 project outwardly and downwardlyfrom the carriage side panel 46. They slide through a slot 90 in a slotsensor 92 which detects their presence within the slot 90, such as byblocking a beam of light. Travel of the front flag 86 and rear flag 88through the slot sensor 92 provides a reference location of the carriage32 to the control system 28.

The top panel 48 of the carriage 32 can rotate about the upper rail 58.A spring 94 between the top panel 48 and side panel 46 biases the toppanel 48 downwardly to hold the cassette 34 within the carriage 32. Adisposing cam 96 sits behind the side panel 46 and aligns with anejecting tab 98 which extends outwardly and downwardly from the toppanel 48 and which can project through an opening 100 in the side panel46 when the top panel 48 rotates upwardly. Such rotation of the toppanel 48 releases its hold upon the cassette 34 and due to the ejectingtab 98 projecting through the opening 100 pushes the cassette 34 out ofthe carriage 32 and into the spent cassette collection box.

The disposing cam 96 controls rotation of the top panel 48. It comprisesa generally triangular shape, having an outwardly facing side 102,forwardly facing side 104 and rearwardly facing side 106. Turning alsonow to FIG. 5, it mounts for rotation upon an upwardly extending spindle108. A spring 110 biases the disposing cam 96 counterclockwise, urgingthe outwardly facing side 102 into contact with an abutment 112. Inwardmovements of the carriage 32 allow the ejecting tab 98 to cam over therearwardly facing side 106 of the disposing cam 96, thus allowing thedisposing cam 96 to rotate clockwise and allow the ejecting tab 98 topass thereby without effecting rotation of the top panel 48. However,outward movement of the carriage 32 causes the ejecting tab 98 to camover the forwardly facing side 104 of the disposing cam 96. During suchmotion contact between the outwardly facings side 102 of the disposingcam 96 and the abutment 112 prevents rotation of the disposing cam 96.The camming of the ejecting tab 98 thus causes it to move laterallytoward the side panel 46 thereby rotating the top panel 48 upwardly andreleasing the cassette 34 from the carriage 32.

Prior to inserting the cassette 34 the carriage 32 is fully retracted toits outward position (to the left as shown in FIG. 5). In this positionalso, a forward end 114 on the lead screw nut 60 engages a stop 116 thuspositively locating the position of the carriage 32. Turning also now toFIG. 6, manual insertion of the cassette 34 causes the carriage 32 tomove inwardly (to the right as shown in FIG. 6) and moves the front flag86 into the slot sensor 92. This movement is preferably caused by thephysical force from inserting the cassette 34, however, a torque orother sensor could be applied to allow the stepping motor 38 to takeover this movement upon feeling the force of the cassette 34 beinginserted into the carriage 32. Allowing this movement to come from theforce of the insertion of the cassette 34 ensures that the cassette 34is fully seated within the carriage 32 before the movement begins.

Once the front flag 86 is read by the slot sensor 92 the stepper motor38 takes over and starts to move the carriage 32 inwardly. Turning alsonow to FIG. 7, during this stage, the scanner 42 scans the barcode 80 onthe cassette 34. The control system 28 interprets the information comingfrom the barcode 80 and determines whether the cassette 34 has been usedin the sterilizer 10 before, whether the cassette contains freshsterilant, and other data as appropriate. Preferably, the information onthe barcode 80 is encrypted to prevent unauthorized parties fromcreating cassettes which may not meet the quality standards necessaryfor proper sterilization.

If the control system 28 rejects the cassette 34 a carriage 32 is movedsufficiently inwardly so as to pass the ejecting tab 98 past thedisposing cam 96 and is then moved back to the insertion position shownin FIG. 5 to eject the rejected cassette 34. If the cassette 34 isaccepted, the carriage 32 continues inward movement to the home positionas shown in FIG. 8 in which the rear flag 88 has just passed out of theslot sensor 92.

Turning also now to FIGS. 9 and 10, the cassette 34 comprises aplurality of cells 118 containing liquid sterilant 120. Variousstructures of a cassette may be employed. The cassette 34 showncomprises a hard outer shell 122, preferably formed of an injectionmolded polymer, such as high impact polystyrene, high densitypolyethylene or high density polypropylene, which encloses theindividual cells 118, the cells 118 being formed of a blow moldedpolymer such as low density polyethylene. However, a more rigid materialcan be used to form the cassette cells 118 in which case the outer shell122 could be omitted. In the cassette 34 shown, an upper aperture 124and lower aperture 126 through the shell 122 allows the upper and lowerneedles 70 and 72 to penetrate the shell. The cell 118 is formed of amaterial easily penetrated by the needles. If the cell 118 is formed ofa more substantial material, a thinning of the material could beprovided at the locations to be penetrated by the needles 70 and 72.

The control system 28 uses the home position of FIG. 8 as a referenceposition for positioning the various cells 118 in front of the extractorsubsystem 40. By moving the carriage 32 a predetermined amount from thehome position a given cell 118 can be brought to face the extractorsystem 40. In FIG. 9, cell one has been placed in front of the extractorsystem 40. Turning also now to FIG. 11, an actuator 128 drives theextractor subsystem 40 toward the cassette 34 causing the upper andlower needles 70 and 72 to penetrate the upper and lower apertures 124and 126 and enter the cell 118. After the needles have fully extended,the air pump 74 drives air into the cell 118 through the upper needle70. The system waits a couple of seconds before starting the air pump 74and opening the valve 76 to ensure proper placement and settling of theneedles within the cell 118. The sterilant 120 flows out through thelower needle 72 and is piped off to the vaporizer 18. After a sufficienttime to extract the sterilant 120, the air pump 74 switches off and theactuator retracts the extractor subsystem 40 from the cassette 34.

The vaporizer 18 connects to the vacuum chamber 14 which allows thelower needle 72 to easily be placed at a pressure below atmospheric.Thus, the pump 74 can optionally be replaced by a valve (not shown) opento atmosphere, in which case the incoming atmospheric pressure air willprovide the driving force to empty the cell 118.

Rather than employ upper and lower needles 70 and 72, one needle havingtwo lumens therethrough would suffice. One of the lumens would providepressurizing gas and one would extract liquid sterilant. A furtheralternative arrangement would be to pierce the cell 118 vertically, orsubstantially so, from an upper part of the cell 118, preferably withsuch a double lumen needle. This would minimize leakage around the holecreated by the needle entering the cell 118. Such entry would also allowthe tip of the needle to come closer to the lowest point of the cell 118for maximum extraction efficiency. If one desired to extract less thanall of the contents of the cell 118, one method would be to position theneedle extracting the sterilant, such as the lower needle 72 or the justmentioned double lumen needle, at the level in the cell 118 down towhich extraction is desired. Liquid sterilant above the position wouldbe extracted and sterilant below would remain. This would beparticularly convenient with the just mentioned vertically travelingneedle.

Turning also to FIG. 12, each time the control system 28 determines thata new dose of sterilant 120 is required, the stepper motor 38 moves thecassette to position the next cell 118 in front of the extractorsubsystem 40 and a new extraction takes place. Multiple extractions maybe employed for a given sterilization cycle. When the cassette 34 hasbeen depleted, the carriage 32 moves towards the insert position thuscausing the ejecting tab 98 to cam over the disposing cam 96 to rotatethe top panel 48 upwardly and project the ejecting tab 98 through theopening 100 to drive the cassette 34 out of the carriage 32 as describedabove and as shown in FIG. 13. The cassette 34 falls into the spentcassette collection box 84 and the carriage 32 returns to the insertionposition as shown in FIG. 5.

The foregoing discussion described the operation of the cassettehandling system in some detail. FIG. 14 shows, in block diagram form,the basic operation of the cassette handling system 12.

The system of reading barcodes on the cassette 34 and spent cassette box84 can be replaced with radio frequency identification tags, commonlyknown as RFID tags. An RFID system 130 is shown in FIG. 15. It comprisesa controller 132 connected via an SPDT reed relay 134 to a cassetteinsertion antenna 136 located on the carriage 32 and a cassette disposalantenna 138 located beneath the spend cassette box 84. Each cassette 34carries a cassette RFID tag 140. Similarly, each spent cassettecollection box 84 carries a collection box RFID tag 142. Preferably, thecontroller 132 comprises a Texas Instruments multifunction reader moduleS4100 and the RFID tags 140 and 42 comprise Texas Instruments RFID tagRI-101-112A each of which are available from Texas Instruments, Dallas,Tex.

The control system 28 (FIG. 1) selects one of the antennas, as forinstance the cassette insertion antenna 136 and sends a signal to therelay 134 to engage this antenna with the RFID controller 132. Theantenna reads the information stored on the cassette insertion RFID tag140 which identifies the cassette 34 and its contents. The informationread is similar to the information read using the barcode, howeverpreferably, the RFID tag 140 has the ability to update the informationstored thereon. Accordingly, additional data such as the filling statusof individual cells 118 within the cassette 34 can be stored on the RFIDtag. Thus, if the cassette 34 is removed and then reinserted into thesterilizer 10, or even into different sterilizer 10, the control system28 can be apprised of the status of each of the individual cells 118within the cassette 34. This allows the reuse of a partially usedcassette 34. Also, since the RFID tag 140 can hold more data than thebarcode 80, more data about the cassette 34, its contents andmanufacturing can be included thereon.

The spent collection box antenna 138 reads the spent collection box RFIDtag 142 to determine the presence or absence of the spent cassettecollection box 84. Other data such as a unique identifier for the box84, the capacity of the box 84, how many cassettes 34 are currently inthe box 84 and how many of the cells 118 therein are not empty can beincluded on the RFID tag 142. The control system 28 can track how manycassettes 34 have been ejected into the box to determine whether it hasroom for more spent cassettes 34. The antenna 138 can also read thecassette RFID tags 140 and count the number of cassettes 34 within thebox 84. When the box 84 is full the control system 28 alerts theoperator, as by a message on a screen. This message can also includeinformation regarding the cassettes 34 within the box 84. For instanceif not all of the cassettes 34 have been completely drained the operatorcan be informed of this to decide if more careful disposal may beindicated.

RFID technology is disclosed in the following U.S. Patents, each ofwhich is incorporated herein by reference: U.S. Pat. Nos. 6,600,420;6,600,418; 5,378,880; 5,565,846; 5,347,280; 5,541,604; 4,442,507;4,796,074; 5,095,362; 5,296,722; 5,407,851; 5,528,222; 5,550,547;5,521,601; 5,682,143 and 5,625,341.

RFID tags typically comprise an antenna and an integrated circuitproduced in a thin form factor so they can be inconspicuously placedupon an object such as the cassette 34. Radio frequency energy sent bythe antennas 136 and 138 induce sufficient current within the antennainside the RFID tags 140 and 142 to power the integrated circuittherein. Some types of RFID tags carry their own power source and havelonger detection ranges, but that adds additional expense and isprobably not justified for the present use.

FIG. 16 shows the memory map for the memory within the RFID tags 140 and142. A 64-bit unique ID (UID) is set at the factory and cannot bechanged. Each RFID tag has its own unique number here. Sixty-four 32-bitblocks can be programmed by the user. These can be populated withinformation such as the manufacture date, expiration date, product ID,serial number, lot numbers, manufacturing location, filling status ofthe cells, strength and type of sterilant, time spent within thesterilizer 10 and the like.

Some sterilants are affected by heat. The RFID tag 140 can optionallyinclude temperature collection instrumentation and update thatinformation on the tag. If design temperature profiles are exceeded,such as a maximum temperature or excessive temperature over a timeperiod, then the cassette 34 can be rejected by the control system 28.Temperature measuring RFID tags are available from KSW-Microtec,Dreseden, Germany and from Identec Solutions, Inc., Kelowna, BritishColumbia, Canada. The interior of the sterilizer 10 where the cassette34 sits may be higher than ambient temperature. Thus, it may bebeneficial to put a maximum residence time (on board shelf life) on thetag 140 or even to update on the tag 140 this time the cassette hasalready spent inside of the sterilizer.

To test sterilant measuring equipment in the sterilizer 10, it may bebeneficial to provide cassettes 34 having water or other fluids withinone or more cells 118. Information regarding the special nature of thecassette 34 and its contents could be written onto the RFID tag.

During a cycle the sterilizer may only require part of the contents of acell 118. For instance, a particular cycle may call for the contents ofone and a half cells. The half filled nature of the cell 118 can bestored and then for the next cycle that cell 118 can be drained.

Preferably, communications between the tag 140 and 142 and thecontroller 132 are encrypted. For instance, the UID can be XORed with aneight-bit master key to form a diversified key for encrypting the data.Encryption algorithms such as the data encryption standard (DES) tripleDES, asymmetrical encryption standard (AES) or RSA security can be usedfor the encryption. The RFID controller 132 reads the data and thealgorithm in the control system 28 decrypts the data to reveal thestored information.

Other methods could be used to communicate between the cassette 34 andthe sterilizer 10. For instance information could be stored magneticallyon the cassette 34, such as with a magnetic encoded strip, and be readby a magnetic reader on the sterilizer. Wireless technology is becomingcheaper every day and it is envisioned that the cassette 34 couldinclude an active transmitter and a power source (i.e. a battery) suchas powered RFID tags or Bluetooth, 802.11b or other communicationstandard.

Further, the sterilizer 10 can be set up to communicate back to acentral source, such as the manufacturer or distributor thereof, andprovide information regarding its performance and the performance of thecassettes 34. Poorly performing cassettes 34 could be identified, as forinstance sterilant monitors in the sterilizer not detecting sterilantduring a cycle thus indicating some failure such as an empty cassette orbad sterilant therein. An improperly manufactured batch of cassettes 34could then be quickly identified and recalled. Such communication couldoccur over telephone, pager or wireless telephone networks or over theInternet.

Turning now also to FIGS. 17 and 18, the spent cassette collection box84 is preferably folded from a single sheet of printed cardboard orother stock. FIG. 17 shows an unfolded blank 150 and FIG. 18 shows theblank 150 folded to form the spent cassette collection box 84.

The blank 150 is divided by a series of fold lines (shown dashed) andcut lines into a bottom panel 152, side panels 154, end panels 156 andtop flaps 158. Folding tabs 160 extend laterally from the side panels154. Additional folding tabs 162 extend laterally from the end panels156. Barcodes 82 are printed on the side panels 154 in a position to bevisible in an upper interior corner of the spent cassette collection box84 when it is folded into the configuration shown in FIG. 18. A pair oftop flap locking tabs 164 extend from the top flaps 158 and fit intoslots 166 in the opposing top flap 158 when the box 84 is closed andinto slots 168 at the intersection of the bottom panel 152 and sidepanel 154 when the box 84 is opened.

To fold the box, the folding tabs 160 on the side panels 154 are foldedupwardly and then the side panels 154 are folded upwardly, therebyaligning the folding tabs 160 with the intersection between the bottompanel 152 and the end panels 156. The end panels 156 are then foldedupwardly and the end panel folding tabs 162 are folded downwardly overthe folding tabs 160. Locking tabs 170 on the end panel folding tabs 162fit into slots 172 at the intersection between the bottom panel 152 andend panels 156.

To place the box 84 into the open position as shown in FIG. 18, the topflaps 158 are folded downwardly to the outside and the locking tabs 164fitted into the slots 168. Once the box 84 is filled with spentcassettes, the top flaps 158 are folded upwardly over the top and thelocking tabs 164 can then be fitted into the slots 166 on the opposingtop flaps 158. This unique folding arrangement allows spent cassettes 34to fall into the open box 84 easily without the top flaps 158 getting inthe way and also allows easy closure of the box 84 once it has becomefilled.

While the invention has been particularly described in connection withspecific embodiments thereof, it is to be understood that this is by wayof illustration and not of limitation, and that the scope of theappended claims should be construed as broadly as the prior art willpermit.

1. A method of delivering a liquid sterilant to a sterilizer comprisingthe steps of: a) piercing a cell of a cassette with a first needlehaving a first lumen; b) flowing a gas into the cell to pressurize thecell relative to a pressure within the first lumen and drive the liquidsterilant out of the cell through the first lumen; and c) flowing theliquid sterilant from the lumen to a vaporizer in the sterilizer.
 2. Amethod according to claim 1 wherein a second lumen through the firstneedle opens into the cell and further comprising the step of injectingthe gas into the cell through the second lumen.
 3. A method according toclaim 1 and further comprising the steps of piercing the cell with asecond needle having a second lumen opening so that the lumen opens intothe cell and injecting the gas into the cell through the second lumen.4. A method according to claim 1 wherein the gas is at atmosphericpressure and the first lumen is at a pressure below atmosphericpressure.
 5. A method according to claim 1 wherein the gas is at apressure greater than atmospheric pressure.
 6. A method according toclaim 1 wherein steps a), b) and c) are repeated with a second cell. 7.A method according to claim 1 wherein the liquid sterilant compriseshydrogen peroxide.
 8. A method according to claim 1 wherein in step a)the needle enters the cell laterally.
 9. A method according to claim 1wherein in step a) the needle enters the cell at an upper portionthereof and travels downwardly therein.
 10. A method according to claim9 and further comprising the step of positioning the first needle sothat the first lumen opens into the cell at or near its lowest pointwhereby to maximize extraction of liquid sterilant from the cell.
 11. Amethod according to claim 1 and further comprising the step ofpositioning the first needle so that the first lumen opens into the cellat or near its lowest point whereby to maximize extraction of liquidsterilant from the cell.
 12. A method according to claim 1 and furthercomprising the step of positioning the first needle so that the firstlumen opens into the cell at a predetermined vertical position andextracting the liquid sterilant above the predetermined position, suchthat less than a total amount of liquid sterilant in the cell is thusextracted.